Plasminogen activator (PA) has been purified to apparent homogeneity (Biochem. 19 (1980) 5463) from Rous sarcoma virus transformed chick embryo fibroblasts (RSVCEF). The purified molecule can now be utilized firstly as an antigen for the production of a specific antibody and secondly as an effector of cellular behavior. The purified molecule will be added to cultures of normal CEF to determine if the properties of normal cells can be altered by a specific molecule which is endogenous to the malignant transformed counterpart of the normal cells. The properties to be tested include induction of DNA synthesis, glucose transport, morphology, microfilament pattern, surface polypeptide pattern, and migratory behavior. These experiments will be conducted in the absence of plasminogen and will indicate if purified PA can catalytically act on cellular substrates independent of its only known natural substrate, plasminogen. Evidence from this laboratory has already indicated that endogenous PA can act on cellular substrates (Cell 17 (1979) 131). Purified proteins including chick fibronectin will also be tested as potential substrates for the purified chick PA. The antibody to PA will also be employed as a unique probe to examine the nature and function of PA in RSV induced malignant transformation, employing the temperature sensitive mutant of RSV. The second part of the proposal will be an examination of the role of PA in the invasive properties of RSVCEF. The chick chorioallantoic membrane system (CAM) and other tumor cell invasion assays have now been established in the laboratory. A detailed inhibitor profile of RSVCEF PA has also been established. The specific inhibitors of PA, the tumor promotor PMA which induces PA, the purified PA itself, and the antibody to PA will be tested in each invasion assay to assess for the first time a direct role for PA in tumor cell invasion. Monitoring tumor cell invasion and growth in the CAM system affords a unique opportunity to examine in vivo avian target tissue with avian tumor cells, in which the latter have been well-characterized in terms of their specific PA molecule and its catalytic manifestation.